Field of the Invention
The invention relates to a mould part and mould for encapsulating electronic components mounted on a carrier. The invention also relates to a method for encapsulating electronic components mounted on a carrier
Such a mould and method from prior art whereby using for instance epoxy resin a package of moulding material can be applied around an electronic component mounted on a carrier such as a lead frame or BGA. One particular application of this technique is encapsulating semi-conductor products, such as chips.
One of the market trends is the mounting on a carrier of encapsulating packages of an ever-increasing area. These packages can be subdivided by sawing during further processing. The drawback of the current gate to a mould cavity is that the filling of larger-area mould cavities calls for higher encapsulating material flow velocities. This in turn may result in the formation of gas inclusions or stresses in an encapsulating material package after curing.
JP 02 0447439 discloses a method and apparatus for forming a resin-sealed package in a cavity with a widely opened gate over one sidewall of the cavity. This results in a short transfer time of the resin without increasing the charging speed of the resin. Although this technique provides an improvement in the filling speed of a mould cavity it is difficult to produce an equal flow speed of the encapsulating material over the whole length of the gate opening, thus giving problems in an equal filling of the mould cavity.
The present invention has for its object to upgrade both the mould and the method of encapsulating electronic components mounted on a carrier whereby high-speed and well-controlled production of larger-area packages of encapsulating material is possible.
To this end the invention provides a mould part. The gate of oblong shape from the runner to the mould cavity herein preferably runs parallel to a contact face of the associated mould part for cooperation with a counter mould part. An advantage of an oblong supply opening is that encapsulating material can be fed simultaneously into the mould cavity over the entire supply opening length. At least one runner debouches into a distribution chamber for encapsulating material, which distribution chamber transposes into the mould cavity by means of the gate of oblong shape to evenly distribute the pressure in the distribution chamber, whereby the encapsulating material will then flow uniformly into the mould cavity along the entire length of the gate. On initiation of an encapsulating operation the encapsulating material will first of all fill the distribution chamber before entering the mould cavity. This enables a large mould cavity to be filled equally with encapsulating material in a relatively short period of time without the flow velocities of the encapsulating material having to be high. The present invention thus enables a package of high-grade encapsulating material of a fairly large area to be manufactured on a controlled way in a brief period of time. Another advantage of the mould part according to the invention is its high flexibility in use. If, for example, a plurality of runners for moulding material open onto a specific mould cavity, they should, for homogeneous filling of the mould cavity, debouch into the mould cavity at positions where they are located close to the electronic components to be encapsulated. This means the positions where the runners open onto the mould cavity depend on the locations of the electronic components to be encapsulated. This is why the prior art causes the mould structure to depend on the orientation of the mounting of the components on the carrier. With gating through an oblong connection in accordance with the invention a mould cavity may be wholly filled irrespective of the orientation of the mounting of the electronic components for encapsulating on the carrier. This enables a wide variety of products to be encapsulated using one single mould. It is only the shape of the carrier and the location at which the packages of encapsulating material have to be arranged which are determined by the mould. A mould part and a mould according the invention are therefore flexible in use.
The oblong gate from runner to mould cavity may have different shapes. It may be straight for opening onto a straight mould cavity face, angular for opening onto a mould cavity angle or for instance curved for opening onto a curved mould cavity face. Although mould cavities are generally substantially rectangular, the present invention can be used irrespective of the mould cavity shape. Partly subject to mould cavity dimensions and the encapsulating material to be used, it is for instance possible to choose a gating via one long side of a mould cavity or a mould cavity angle. An alternative is to fit a mould cavity with a plurality of oblong gates.
This encapsulating material distribution chamber is preferably recessed further into said mould part than the gate of oblong shape. A threshold-like elevation is thus positioned between distribution chamber and mould cavity, making that the distribution chamber will be filled before the encapsulation material enters the mould cavity. An additional advantage is that it is possible to manufacture comparatively thin packages of encapsulating material, since the encapsulating material enters the mould cavity as a thin layer.
While the mould cavity is being filled with encapsulating material, the gas present in the mould cavity should be able to escape from the mould cavity. To this end the mould cavity is provided with a gas discharge opening, which is also oblong in shape. A preferred embodiment of the mould cavity is provided with a plurality of gas discharge openings of which the gates run substantially parallel to the gate of oblong shape. The encapsulating material flows through the mould cavity across a wide front and, in order to prevent the formation of gas inclusions, the gas should be able to escape from the mould cavity at various positions. This is found to be a particularly advantageous option when the discharge opening is oblong-shaped and runs substantially parallel to the front of the flowing encapsulating material in the mould cavity.
The invention also provides a mould for encapsulating electronic components mounted on a carrier, which mould comprises at least one mould part as specified above. The above described mould part functions only in co-action with a counter mould part.
The invention also provides a method for encapsulating an electronic component mounted on a carrier. The moulding material is herein preferably fed into the mould cavity as a thin layer with a substantially constant front. The wide front of encapsulating material will be forced over the electronic components to be encapsulated in more or less constant manner, which is why the orientation of the electronic components on the carrier is irrelevant to the choice of a specific mould. The other advantages of this method have already been described with reference to the mould part according the invention.